[ios, macos] Add overlays property to MGLMapView (#8617)

* Add `overlays` property to `MGLMapView.mm`

Implemented by filtering the `annotations` property for
annotations that conform to `MGLOverlay` protocol.

* Handle `nil` case when returning overlays

* Add basic documentation for `overlays` property

Copied verbatim from `annotations` property. Changed types.

* Add `overlays` property to iOS sdk

Implementation is identical to the one in macOS SDK.

* Match curly braces style

* Make `overlays` property `nonnull` on iOS

* Make `overlays` property `nonnull` on macOS

* Make cosmetic changes

* [ios, macos] Moved changelog entry to master

1 files changed, 16 insertions, 0 deletions

diff --git a/platform/ios/src/MGLMapView.mm b/platform/ios/src/MGLMapView.mm
index 8cba1187ea..d97c0b6602 100644
--- a/platform/ios/src/MGLMapView.mm
+++ b/platform/ios/src/MGLMapView.mm
@@ -3531,6 +3531,22 @@ public:
     }
 }
 
+- (nonnull NS_ARRAY_OF(id <MGLOverlay>) *)overlays
+{
+    if (self.annotations == nil) { return @[]; }
+
+    NS_MUTABLE_ARRAY_OF(id <MGLOverlay>) *mutableOverlays = [NSMutableArray array];
+
+    [self.annotations enumerateObjectsUsingBlock:^(id<MGLAnnotation>  _Nonnull annotation, NSUInteger idx, BOOL * _Nonnull stop) {
+        if ([annotation conformsToProtocol:@protocol(MGLOverlay)])
+        {
+            [mutableOverlays addObject:(id<MGLOverlay>)annotation];
+        }
+    }];
+
+    return [NSArray arrayWithArray:mutableOverlays];
+}
+
 - (void)addOverlay:(id <MGLOverlay>)overlay
 {
     [self addOverlays:@[ overlay ]];